Many types of curtains, blinds, and screens have been developed for the purpose of blocking entry of solar radiation or glare into vehicles. Many prior designs have required permanent installation of a shade or screen, which may be collapsible when use is not desired. Some devices are foldable into the collapsed configuration, while others retract to a non-use position. The need for window screens that can be secured in place temporarily and folded or rolled into a small package for storage has also been recognized. Prior devices of interest in the field include those described in U.S. Pat. Nos. 1,018,498; 2,305,677; 2,804,135; 2,855,241; and 3,003,812.
U.S. Pat. No. 4,202,396 discloses a sunshield intended to be placed inside the windshield of an automobile while the automobile is not in use. The shield is made of corrugated cardboard scored to permit accordion folding of the large rectangular sheet into a smaller package for storage during operation of the vehicle. The package is expanded and slipped behind the rear view mirror to block the windshield, and the sun visors may also be used to hold the shield in place.
In order to prevent the multiple panel device disclosed in this patent from collapsing during use, the foldable connections between panels extend at right angles from the lower margin of the windshield, that is, vertically. Thus, the shield has no transverse rigidity unless it is folded across all the accordion folds, which reduces the ability of the device to adapt to different windshield shapes and widths. To accommodate the fact that most modern cars have windshields that are narrower at the top than at the bottom, the device must partially collapse at the top. The weight distribution of the installed device is thereafter unbalanced, with the result of a tendency of the device to fall away from the window.
Another disadvantage of the accordion folded shield is the number of folds required to collapse the device. Seven to nine folds are shown in the patent. Furthermore, the surface available for display of advertising is quite small when the shield is collapsed.
While the sun screen disclosed in copending parent application Ser. No. 193,397, filed May 12, 1988, which is incorporated by reference in its entirety herein, is adequate for the purposes described, problems have arisen from the fold configuration in which an inner fold rests tightly within an outer fold. It has been found that there is a strain placed on the outer fold line by the inner fold being jammed into the outer fold when the sun screen is collapsed. This strain can cause premature tearing of the outer fold line. There is a need then, for a sun screen which has the folds designed to avoid such strain when the screen is collapsed.